The field of the invention is a process for preparing aqueous dispersions of synthetic resins and an apparatus for the production of these dispersions.
The invention is particularly concerned with the preparation of aqueous synthetic resin dispersions by precipitating the synthetic resins from their solutions in water miscible solvents with water. The solutions may also contain pigments, fillers, and additives and the precipitation is simultaneously mechanically stressed by milling means, the precipitated solids are subsequently separated and uniformly distributed in an aqueous medium.
The state of the art of such methods may be ascertained by reference to U.S. Pat. Nos. 2,831,840; 2,854,426; 2,977,351; 3,090,774; 3,432,483; 3,544,540; 3,862,103; and 4,202,965, the disclosures of which are incorporated herein.
With regard to synthetic resin systems used in coating processes, the particle size distribution of the solid ingredients affects greatly the property profile of many liquid system properties, for instance the stability of sedimentation, applicability, flow properties during film formation and the properties of the deposited and hardened films, for instance the color intensity and the gloss. Accordingly, specific distributions of particle sizes are required for specific products and applications, where these distributions should be below 10 microns for primer surfacers, motor vehicle primers and automobile top coats. The particle sizes of synthetic resins in aqueous synthetic resin dispersions should also be of the same order of magnitude as the particle sizes of the pigments for these fields of application. This is not achieved however when synthetic resin solutions in organic solvents are atomized with gases, superheated steam, air or natural gas. The atomized products then are dried and the solid, solvent-free synthetic resin particles so obtained are dispersed in water to form a synthetic resin dispersion. The required particle sizes and a uniform distribution of grain sizes again are not achieved when a synthetic resin solution in organic solvents is distributed in water in an agitator, whereby the solid is precipitated. Again no good results are obtained when a synthetic resin solution in organic solvents is blown by means of jet nozzles into water, the solid being precipitated in this manner.